I have 'Resouce' dataobject as below with attachment as has_one relation. I would like to delete the attachment when 'resource' object is deleted.

But what I get is Fatal error: Call to a member function delete() on a non-object in

<?php
class Resource extends DataObject
{
private static $db = array (
'Name' => 'Varchar(200)',
'Description' => 'Text',
'Category' => "Enum('Data, Drafts, Drawings, Reports, Images, Other')",
'SortOrder' => 'Int'
);

private static $has_one = array (
'Attachment' => 'File',
'ResourcePage' => 'ResourcePage'
);

public function onBeforeDelete()
{
$myAttachment = $this->Attachment();
$file = DataObject::get_by_id('File', $myAttachment->ID); //we have to make sure it is a Dataobject object
$file->delete();
$file->destroy();
return parent::onBeforeDelete();
}

}

Does it mention the what line of code is throwing the error as you are deleting a object which removes the object from the cache and then you are trying to call destroy on a deleted object.

It might be and idea to wrap the delete and destroy in a if statement checking if the object actually exists before trying to delete it.

if ($file && $file->exists()) {
        $file->delete();
        $file->destroy();
}

Yes Kirk, you are right 'if' condition was missing.

The error was due logical, I should have checked whether file exists, before doing delete method

now my code after updation
public function onBeforeDelete()
{
$myAttachment = $this->Attachment();
$file = DataObject::get_by_id('File', $myAttachment->ID); //we have to make sure it is a Dataobject object
if ($file) {
$file->delete();
}
return parent::onBeforeDelete();
}

thanks Kirk